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Allergic contact dermatitis (ACD) is a type 4 or delayed-type, hypersensitivity response (DTH) by an individual’s immune system to a small molecule (< 500 daltons), or hapten, that contacts a sensitized individual’s skin.[1] The initial or induction phase of ACD occurs when the hapten combines with a protein to form a complex that leads to the expansion of an allergen-specific T cell population; this process is known as sensitization. During the elicitation phase, re-exposure to the antigen leads to the development of dermatitis.[2] ACD accounts for 20% of contact dermatoses, and allergens differ greatly based upon geography, personal habits and hobbies, and often, the types of preservatives that are legally permissible, such as quaternium-15 in the United States but not Europe.[3]

A good clinical evaluation of allergic contact dermatitis (ACD) involves a detailed history and physical. The morphology and location of the dermatitis is often the best indicator of the offending agent. Patch testing can be performed to help confirm the diagnosis. If the diagnosis is still not certain, a skin biopsy usually demonstrates spongiosis.[8]